The general aim of the investigation is to determine some of the factors that influence axonal growth, either during regeneration following injury or during ontogenetic development. The basic questions that underlie this study are (1) what are the stimuli that initiate axonal growth, (2) what factors influence the rate of elongation of the growing axon, and (3) what interactions may occur between such an axon and the cells with which it comes in contact. The answers to these questions are important for an understanding of the developmental dynamics of the embryonic and neonatal nervous system, and the prospect is that they may provide clues to procedures for promoting the repair of damaged nervous tissue. Some of the specific subjects of investigation are the mechanisms of axonal transport of materials in normal and regenerating nerve cells, the transfer of materials from one nerve cell to another, and alterations in protein metabolism in the course of regeneration. Other studies are devoted to the examination of axonal outgrowth, in order to determine the properties of the emerging axons and to find ways of enhancing their outgrowth.